The present invention relates to an intake system for internal combustion engines and, more particularly, to an engine intake system employing a single or a plurality of fuel injectors disposed in an induction passage, upstream of a throttle valve to inject jets of fuel into the induction passage.
In, for example, Japanese pre-examination patent publication No. 79666/83, an intake system for an internal combustion engine is proposed which includes a single or plurality of fuel injectors for injecting jets of fuel into an inducation passage upstream of a throttle valve disposed therein. The throttle valve is rotatable about the axis of a throttle shaft between idle and fully opened positions. When the engine is in an idle operation, the throttle valve is inclined to the axis of the induction passage and has upstream and downstream edge portions slightly spaced from the inner peripheral surface of the induction passage to cooperate therewith to define narrow gaps through which air and the injected fuel particles are allowed to pass toward engine cylinders. A part of the air and fuel particles then whorls toward the center of the underside of the throttle valve due to vacuum immediately downstream of the throttle valve whereby vortices are generated downstream of the throttle valve. The fuel particles suspended in the whirling air streams tend to gather at a central zone of the vortices to form a mass of liquid fuel. When the liquid mass has grown to a certain size, a part of the liquid mass is separated therefrom to form drops which are sucked into the engine. For this reason, the fuel is not fed into the engine at a uniform rate during an entire idle operation, resulting in an unstable engine idle operations and difficulties in the emission control as will be discussed more fully hereinbelow.